Knob with different gear ratios

ABSTRACT

A knob adjustment device particularly for adjusting the temperature in valve units for water-heating apparatus. The device comprises a geared transmission interposed between the knob and an operating member of the valve unit in order to transmit a rotary movement to the member about its own axis as a result of a rotation of the knob. The geared transmission includes a reduction mechanism with a variable transmission ratio such that, for a first angular portion and a second angular portion of the rotation of the knob, the member is rotated with respective different transmission ratios (T 1 ,T 2 ).

This application is a U.S. national-phase application of PCTInternational Application No. PCT/EP01/07600.

TECHNICAL FIELD

The present invention relates to a knob adjustment device, particularlyfor temperature adjustment in water-heating apparatus. The inventionrelates, in particular but not exclusively, to the field ofwater-heating apparatus such as, for example, a domestic water-heaterhaving a thermostatic valve unit with a knob adjustment device foradjusting the temperature to which the water is to be heated.

BACKGROUND ART

In these units it is desirable to operate with a single valve seatassociated with a respective closure element which has both the functionof shutting off the gas flow (ON/OFF) and the function of adjusting theflow to achieve the water temperature desired by the user. In thisconnection, the valve unit has a knob adjustment device operativelyconnected to the closure element by a control member with which the usercan enable the function of lighting a pilot burner or of shutting offthe gas-flow (OFF) and, in addition, can select a preselectedwater-temperature value.

When the above-mentioned functions are incorporated in a single device,it is also desirable to be able to perform these functions at most by asingle rotation of the knob, in order to achieve quicker and easier useby the user. However, in addition to the angular temperature-selectionband (normally an adjustment within the range between approximately 30°C. and 70° C. is required), it is therefore necessary also to provide anangular band on the knob for regulating the shut-off (OFF) andpilot-burner lighting points. This therefore reduces the angular bandavailable for temperature selection, which translates into a lowerdegree of resolution within the above-mentioned range of betweenapproximately 30° C. and 70° C. such that the user cannot adjust thetemperature with a sensitivity, for example, with variations on theorder of one degree centigrade in the preselected temperature values.

The problem which the present invention solves is that of providing aknob adjustment device which is designed structurally and functionallyso as to overcome the disadvantages explained with reference to theprior art mentioned.

BRIEF DESCRIPTION OF DRAWINGS

The characteristics and the advantages of the invention will becomeclearer from the following detailed description of a preferredembodiment thereof, described by way of non-limiting example, withreference to the appended drawings, in which:

FIG. 1 is a schematic perspective view of a valve unit equipped with aknob adjustment device formed in accordance with the present invention,

FIGS. 2 and 3 are a perspective view and a plan view from below, of theknob adjustment device of FIG. 1, respectively, and

FIG. 4 is a graph showing the rules governing temperature variation as afunction of the angular rotation of the knob device of the previousfigures.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, a valve unit, generally indicated 1, isequipped with a knob adjustment device 2 formed in accordance with theinvention. In the embodiment described, the valve unit 1 is of thethermostatic type and is intended mainly for the adjustment and controlof the water temperature in heating apparatus, for example, in domesticwater-heaters. However, the device according to the invention isintended also to be usable in other fields, although the field indicatedrepresents a preferred selection.

The valve unit 1 has an element 3 sensitive to the variation of thewater temperature and operatively connected to a closure element, notshown, in order to cause the latter to close/open a respective valveseat, also not shown, inside the valve unit 1.

The knob 2 is mounted so as to be rotatable on the valve unit 1 about arotation axis X and is kinematically connected, by a geared transmissionsystem, to an operating member 4, also supported so as to be rotatableon the valve unit 1, about a rotation axis Y. The axes X and Y areperpendicular to one another.

The operating member 4 is in turn associated with an actuator ofconventional type which acts on the closure element of the valve unit 1in order to perform the functions of shutting off the main flow of gasthrough the valve unit 1 as well as of adjusting the temperature valueby the thermostatic closure of the respective valve seat when thepreselected temperature set by the user is exceeded.

More particularly, the functions of temperature adjustment, of enablinga pilot burner associated with the heating apparatus to be lit, as wellas of completely shutting off the gas flow (OFF point) supplied to thevalve unit 1, are combined in the knob 2.

In the knob 2, the geared transmission system is intended to transmit arotary movement to the operating member 4, about its own axis Y, as aresult of a rotation of the knob 2 about the axis X.

The geared transmission system is of the crown-wheel and pinion type andcomprises a pair of coaxial crown wheel sectors 5, 6 fixed for rotationwith the knob 2, as well as a pinion 7, coaxial and fixed for rotationwith the operating member 4, and capable of meshing with the crown wheelsectors 5, 6.

The crown wheel sectors 5, 6 are of the type with face teeth and extendconcentrically substantially as extensions of one another but havingdifferent respective diameters.

The sectors 5, 6 are also spaced apart circumferentially in a mannersuch that the pinion 7 meshes alternatively with one or other of thecrown wheel sectors 5, 6.

Moreover, an intermediate tooth 8 (or several teeth), interposed betweenthe crown wheel sectors 5, 6 and extending concentrically with thesectors 5, 6 along an arc having a diameter between the diameters of thesectors, can also mesh with the pinion 7.

The tooth 8, as well as the crown wheel sectors 5, 6, are spaced apartcircumferentially. The angular distances between the tooth 8 and therespective ends of the sectors 5, 6 closest to the tooth are indicated Aand B in FIG. 3 and the angular amplitudes of the crown wheel sectors 6and 5 are indicated C and D.

For a first angular portion and a second angular portion which areconsecutive and correspond, respectively, to the sectors 5 and 6, thepinion 7 is thus rotated by the knob 2 with a first transmission ratioand with a second transmission ratio T1, T2, respectively (defined asthe ratio between the diameter of the pinion 7 and the diameter of therespective crown wheel sector 5, 6).

According to a preferred characteristic of the device according to theinvention, the transmission ratio T1 is selected so as to beapproximately three times the transmission ratio T2. Moreover, thetransmission ratio, indicated T3, between the tooth 8 and the pinion 7is selected so as to have an intermediate value between the transmissionratios T1 and T2.

The graph of FIG. 4 shows the curve of the temperature (on the ordinate)as a function of the angular rotation band provided on the knob 2 (onthe abscissa).

The angular amplitude D is representative of the band for the selectionof the temperature within the preselected range of approximately 30° C.to 70° C. and the slope of the curve (FIG. 4) in this portion iscorrelated directly and proportionally with the transmission ratio T2with which the operating member 4 is rotated by the knob 2 along thecrown wheel sector 5.

The angular amplitude C, on the other hand, is representative of theangular band required to set the temperature for the opening of the maingas duct at a temperature lower, by a suitable safety margin, than theminimum temperature of use of the apparatus. In this portion, the slopeof the curve is correlated directly and proportionally with thetransmission ratio T1 by which the operating member 4 is rotated by theknob 2 along the crown wheel sector 6.

It will be noted that the change in transmission ratio enables aconsiderably smaller angular band to be achieved for lighting andshutting off (angular distance C) than can be achieved with equaltransmission ratios (equal to T2).

All of the above-mentioned functions implemented in the knob 2 can thusbe set by the user within a single rotation of the knob. A preferredvalue for the angular rotation of the knob corresponding to the sum ofthe angular distances and amplitudes A, B, C, and D is between 225° and340° and is preferably selected so as to be 315°.

Moreover, the temperature selection band (the angular amplitude D) canadvantageously be kept within an angular rotation of the knob 2 on theorder of about 150° so as to permit an adequate resolution and greatersensitivity in the setting of the temperature values by the user. Theangular amplitude C is consequently reduced to a value of about 120° byvirtue of the provision of the transmission ratio T1.

It will also be noted that the changeover of the pinion 7 between itsmeshing with the crown wheel sector 6 and with the sector 5 takes placevia an intermediate meshing with the tooth 8 so as to permit smootherand more continuous rotation of the knob 2. In fact, the pinion 7 isarranged not to mesh with both of the crown wheel sectors 5, 6 at thesame time but changes over between the sector 6 and the tooth 8 andbetween the tooth 8 and the sector 5 by respective successive meshings.The discontinuity of rotation due to the different peripheral velocitiesof the mutually meshed teeth during the instantaneous change oftransmission ratio is thus considerably reduced. The provision of theintermediate transmission ratio T3 thus reduces the effects due to thediscontinuity of rotation and advantageously enables a ratio T1approximately three times the ratio T2 to be achieved.

The invention thus solves the problem set, achieving the advantagesmentioned above.

In particular, the knob adjustment device of the invention enables allof the adjustment and temperature-selection functions provided for to beincorporated in the valve unit 1 with an operative angular band lessthan or equal to one complete rotation of the knob 2, for easier andquicker use by the user, at the same time ensuring an adequate degree ofresolution and sensitivity for the user in the selection of thepreselected temperature value.

1. A knob adjustment device for adjusting the temperature in valve unitsfor water-heating apparatus, the valve units having a rotatable knob andan operating member, the device comprising: a geared transmissioninterposed between the knob and the operating member of the valve unitin order to transmit a rotary movement to the operating member about afirst axis as a result of a rotation of the knob, the gearedtransmission including a reduction mechanism with a variabletransmission ratio such that, for a first and a second angular portionof the rotation of the knob, the operating member is rotated withrespective and different first and second transmission ratios (T₁, T₂),the reduction mechanism including (i) a pinion fixed for rotation withthe operating member, (ii) a pair of crown wheel sectors having faceteeth, coaxial with and fixed for rotation with the knob, the crownwheel sectors being concentrically extended, with respective differentdiameters and respective, circumferentially spaced apart ends, and beingable to mesh with the pinion, and (iii) at least one intermediate toothradially disposed in a position between the crown wheel sectors andcircumferentially disposed in a position between the spaced apart crownwheel sector ends, and able to mesh with the pinion.
 2. A knobadjustment device for adjusting the temperature in valve units forwater-heating apparatus, the valve units having a rotatable knob and anoperating member, the device comprising: a geared transmissioninterposed between the knob and the operating member of the valve unitin order to transmit a rotary movement to the operating member about afirst axis as a result of a rotation of the knob, the gearedtransmission including a reduction mechanism with a variabletransmission ratio such that, for a first and a second angular portionof the rotation of the knob, the operating member is rotated withrespective and different first and second transmission ratios (T₁, T₂)the reduction mechanism including (i) a pinion fixed for rotation withthe operating member, (ii) a pair of crown wheel sectors having faceteeth, coaxial with and fixed for rotation with the knob, the crownwheel sectors being concentrically extended, substantially as extensionsof one another with respective different diameters, and being able tomesh with the pinion, and (iii) at least one intermediate tooth radiallydisposed in a position between the crown wheel sectors and able to meshwith the pinion, the crown wheel sectors and the at least oneintermediate tooth are spaced apart circumferentially in a manner suchthat the pinion meshes alternatively with one or the other of therespective crown wheel sectors or with the at least one intermediatetooth.
 3. The device according to claim 1, in which the at least oneintermediate tooth extends concentrically with the crown wheel sectorsalong an arc with a diameter having an intermediate value between thediameters of the crown wheel sectors.
 4. The device according to claim1, in which the crown wheel sectors and the at least one intermediatetooth have a circumferential extent such that the operating member isrotated for a first angular portion and a second angular portioncorresponding with the respective first and second transmission ratios(T₁,T₂), the first transmission ratio (T₁) between the first crown wheelsector and the pinion being approximately three times the secondtransmission ratio (T2) between the second sector and the pinion.
 5. Thedevice according to claim 4, in which the transmission ratio between theintermediate tooth and the pinion is an intermediate ratio (T₃) betweenthe first and second transmission ratios (T₁,T₂) of the crown wheelsectors.
 6. The device according to claim 2, in which the at least oneintermediate tooth extends concentrically with the crown wheel sectorsalong an arc with a diameter having an intermediate value between thediameters of the crown wheel sectors.
 7. The device according to claim2, in which the crown wheel sectors and the at least one intermediatetooth have a circumferential extent such that the operating member isrotated for a first angular portion and a second angular portioncorresponding with the respective first and second transmission ratios(T1,T2), the first transmission ratio (T1) between the first crown wheelsector and the pinion being approximately three times the secondtransmission ratio (T2) between the second sector and the pinion.
 8. Thedevice according to claim 7, in which the transmission ratio between theintermediate tooth and the pinion is an intermediate ratio (T₃) betweenthe first and second transmission ratios (T₁,T₂) of the crown wheelsectors.